Ultrasonic welding and assembly of engineering plastics

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COPYRIGHT: All rights reserved, in particular for reproduction and copying, and for distribution as well as for translation. No part of this publication may be reproduced or processed by means of electronic systems, reproduced or distributed (by photocopying, microfilm or any other process), without written permission by Ticona. © 2004 Ticona GmbH, Kelsterbach NOTICE TO USERS: To the best of our knowledge, the information contained in this publication is accurate, however we do not assume any liability whatsoever for the accuracy and completeness of such information. The information contained in this publication should not be construed as a promise or guarantee of specific properties of our products. Further, the analysis techniques included in this publication are often simplifications and, therefore, approximate in nature. More vigorous analysis techniques and prototype testing are strongly recommended to verify satisfactory part performance. Anyone intending to rely on any recommendation or to use any equipment, processing technique or material mentioned in this publication should satisfy themselves that they can meet all applicable safety and health standards. It is the sole responsibility of the users to investigate whether any existing patents are infringed by the use of the materials mentioned in this publication. Properties of molded parts can be influenced by a wide variety of factors including, but not limited to, material selection, additives, part design, processing conditions and environmental exposure. Any determination of the suitability of a particular material and part design for any use contemplated by the user is the sole responsibility of the user. The user must verify that the material, as subsequently processed, meets the requirements of the particular product or use. The user is encouraged to test prototypes or samples of the product under the harshest conditions to be encountered to determine the suitability of the materials. Material data and values included in this publication are either based on testing of laboratory test specimens and represent data that fall within the normal range of properties for natural material or were extracted from various published sources. All are believed to be representative. These values alone do not represent a sufficient basis for any part design and are not intended for use in establishing maximum, minimum, or ranges of values for specification purposes. Colorants or other additives may cause significant variations in data values.

We strongly recommend that users seek and adhere to the manufacturer’s current instructions for handling each material they use, and to entrust the handling of such material to adequately trained personnel only. Please call the numbers listed for additional technical information. Call Customer Services at the number listed for the appropriate Material Safety Data Sheets (MSDS) before attempting to process our products. Moreover, there is a need to reduce human exposure to many materials to the lowest practical limits in view of possible adverse effects. To the extent that any hazards may have been mentioned in this publication, we neither suggest nor guarantee that such hazards are the only ones that exist. The products mentioned herein are not intended for use in medical or dental implants. Ticona GmbH Information Service Tel. +49 (0) 180-584 2662 (Germany) +49 (0) 69-305 16299 (Europe) Fax +49 (0) 180-202 1202 (Germany and Europe) e-mail infoservice@ticona.de Internet www.ticona.com

HostaformAcetal copolymer (POM)

HostacomReinforced polypropylene (PP)

CelanexPolybutylene terephthalate (PBT)

Hostalen GURUltrahigh molecular

weight polyethylene (PE-UHMW)

FortronPolyphenylene sulphide (PPS)

VectraLiquid crystal polymers (LCP)

= registered trademark

Contents

1. Introduction 4

2. Design and operation of anultrasonic welding unit 4

3. Ultrasonic welding ofHoechstengineering plastics 5

3.1 Requirements for optimumultrasonic welds 5

3.2 Factors affectingwelding properties 6

3.2.1 Effect of the moulding compound 7

3.2.1.1 Effect of melt viscosity 7

3.2.1.2 Effect of pigments 7

3.2.1.3 Effect of reinforcing materialsand elastomer additions 8

3.2.2 Effect of moulded part design 9

3.2.3 Welding equipment and

welding conditions 9

3.2.3.1 Requirements for the welding equipment 9

3.2.3.2 Effect of welding conditions 9

4. Procedure for optimizing welding conditions 10

5. Designing the joint 11

5.1 Different joint designs 11

5.1.1 Joints with conical and knob-shapedenergy directors 1 1

5.1.2 Joints with roof-shapedenergy directors 1 1

5.1.2.1 Weld design for larger components 12

5.1.3 Joint designs for pinch welds 12

5.1.3.1 Double pinch weld with symmetricaljoint surfaces 13

5.1.3.2 Double pinch weld with asymmetricaljoint surfaces 13

6. Notes on ultrasonic welding of moulded partsmade from Hoechst engineering plastics 1 4

6.1 Hostaform (POM) 14

6.2 Hostacom (reinforced PP) 15

6.3 Celanex (PBT) 16

7. Ultrasonic assembly ofperformance polymers 16

7.1 Fortron (PPS) 16

7.2 Vectra (LCP) 17

8. Other ultrasonic assembly methods 17

8.1 Riveting 17

8.2 Flanging 19

8.3 Staking 19

8.4 Insertion of metal parts 19

9. Examples of applications 22

9.1 Sewing machine control part 22

9.2 Time control mechanism for a toaster 22

9.3 Disposable cigarette lighter 22

9.4 Pneumatic control element 23

9.5 Mixer tap regulator 23

9.6 Example of welding cycle time

calculation 24

10. Literature 24

1. Introduction 2. Design and operation ofan ultrasonic welding unit

Homogeneous jointing of injection moulded or extrusionblow moulded thermoplastic components by ultrasonic

welding is a cost-effective technique which has provedparticularly suitable for long runs because of the veryshort welding cycles.

Ultrasonic welding is an ideal process for jointing cigarette lighter tanks, valve bodies and small containers,assembling parts for electrical equipment and for use in

the automotive and household appliance industries. Withultrasonic welding, high-strength, liquid- and gas-tightjoints can be produced.

The technology has been developed to the stage where

on standard equipment (e.g. up to a maximum generatoroutput of 4 kW), welds up to about 120 mm in lengthcan be produced. Special equipment with combined

vibrating systems make it possible to weld even greaterlengths.

The Hoechst engineering plastics Hostaform, Celanexand Hostacom and the performance polymers Fortronand Vectra have been used successfully in the manufacture of ultrasonically welded components for manyyears. It should be noted that the most suitable type ofweld and welding method depend not only on the mate

rial but also on the design of the finished part and on the

requirements it has to meet. Trial results relate exclusive

ly to the given test specimen geometry and machine con

ditions. Even slight deviations can lead to differentresults. It is therefore almost impossible to draw generalconclusions. For critical applications we recommend

contacting us first.

The principle of ultrasonic welding involves converting(vibrating) energy into heat energy which melts the plasticat the joint surfaces. In an ultrasonic converter, high-frequency alternating current (20 - 50 kHz) is trans

formed into mechanical vibration which are transmittedvia an ultrasonic horn*) into an energy director on one

of the joint surfaces (fig. 1, detail A, and fig. 2). There the

vibrating energy is concentrated in the joint and the jointsurfaces are heated up directly to melting temperature.

Fig. 1: Diagram showing principle of an ultrasonic

welding unit (piezoelectric operation)

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1 Detail "A"

1 Ultrasonic converter }2 Adaptor (amplitude transformer) f resonance unit3 Ultrasonic horn J4 Top part5 Bottom part6 Jig for the bottom part7 Energy director$ Travel

'") Note: In view of the high stresses involved, the ultrasonic horn is made of titanium or high strength aluminium alloys.

The parts being welded are pressed together to obtain the

required welding pressure (horn travel I, see fig. 1, can be

mechanically restricted). The contact pressure is infinitelyvariable.

Various equipment parameters influence the quality ofthe weld:

vibration amplitude,contact pressure,welding time,welding distancehold time (cooling time)

The vibration amplitude can be altered within certainlimits to suit the material and joint design by usingadaptors of different sizes (amplitude transformation),see 2 in fig. 1.

The resonance unit of an ultrasonic system consists ofthe ultrasonic converter, the adaptor and the horn.

3. Ultrasonic welding ofHoechst engineering plastics

3.1 Requirements for optimum ultrasonic welds

Correct joint design is essential for optimum welding(see section 5). The joint must be adequate for the functionof the weld.

It should be noted that

the joint surfaces should normally be positioned lessthan 6 mm from the horn tip (fig. 2). In ultrasonic

welding of Hostaform mouldings, the distance can

be > 6 mm, i.e. at long range; due to Hostacom's highdamping capacity, the distance between the horn and

welding seam should be < 3 mm.

the vibratory energy should be concentrated locallyand if possible should only be effective locally (function of an energy director),

Fig. 2: Positioning of joint surfaces at close range(: 6 mm)

1 Horn2 Top part3 Energy director4 Bottom part

the parting line should be designed to facilitate the

welding operation and not to impair the functioningof the component (figs. 3 and 4).the parts to be welded should be dimensionally stable,i.e. the walls which receive the ultrasonic energyshould be of adequate thickness (e. g. to prevent the

diaphragm effect, fig. 4, i.e. sympathetic vibration ofareas not involved in the welding operation I),corners, edges and transitions should be adequatelyradiused (to prevent notch effect),welds should as far as possible be arranged in a singleplane (contact surface) at right angles to the horn axis

(fig. 3)

Fig. 3: Design of the parting line Fig. 5: Design of contact area "a"

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Fig. 6: Clearance S required for the joint parts andminimum alignment overlap Z

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Fig. 4: Wall thickness design

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the two parts should be perfectly aligned so that theyremain in position when vibratory energy is applied.The alignment overlap should not be less than 1 mm

(fig. 6).projecting pins, ribs, tabs etc. are prone to sympatheticvibration during ultrasonic welding and may thereforemelt and be damaged. This can be countered by usinglarger radii, additional supports or elastic pads,the contact surface of the horn leaves permanent marks

on high-gloss mouldings. This problem can largely be

avoided by interposing LDPE sheets between the horn

and part.

the horn contact area should be flat and adequatelylarge because with too small an area the ultrasonic

energy flow will be impeded (fig. 5),the parts to be joined should fit together with a suit

able clearance, i.e. they should not pinch but on the

other hand the clearance should not be too great(fig. 6); precision injection moulding is recommended,

3.2 Factors affecting weldingproperties

To find the right solution to welding problems, a number

of important factors have to be taken into consideration.These concern material quality, the method used to make

the joint, welding equipment and welding conditions.

3.2.1 Effect of the moulding compound 3.2.1.1 Effect of melt viscosity

As compared with amorphous plastics (PS, ABS, PC,PMMA etc.) partially crystalline thermoplastics requiremore energy to plasticize (melt) the joint faces. This is

basically due to their greater heat of fusion and generallyhigher melting point or range. Furthermore, energy propagation may be impeded in most partially crystallinethermoplastics by their high damping capacity.

This generally means longer welding times and in somecases a higher generator output. Fig. 7 shows the mechanical loss factor curve (which describes damping capacity) as a function of temperature for Hostacom and ABS.

Fig. 7: Mechanical loss factor curve as a function oftemperature for Hostacom (reinforced PP) and ABS(torsion pendulum test according to DIN 53 445)

-160 -120 -80 -40 0 40 80 120 160

Temperature

Provided these properties and requirements are givendue consideration, components produced from partiallycrystalline thermoplastics can be ultrasonically welded,particularly by the close-range method (see section 2).

Suitability for welding and energy transmission lossescan be influenced by additives such as processing aids,pigments, lubricants, reinforcing materials and elastomeradditions.

The effect of these additives on welding properties hasbeen studied with test pieces. The results obtained applyfor the specified test conditions.

Deviating results may be obtained with mouldings of different geometrical shape and welding conditions chosenaccordingly.

Hoechst engineering plastics are produced with various

degrees of polymerization. The grades therefore differin molecular weight and this factor coupled with melt

viscosity has an effect on welding properties. Fig. 8 showsthis using the example of Hostaform. Given the same

welding data, welding time, contact pressure and holdtime, the strength of ultrasonically welded joints varies

according to the Hostaform basic grade.

Fig. 8: Effect of the melt viscosity of Hostaform basicgrades on the strength of welded joints

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J A range of scatter

These variations in the strength of welded joints according to grade can, however, be compensated by carefulselection of welding conditions, i. e. by optimization of

vibration amplitude (use of different-sized adaptorsor amplitude transformers, see fig. 1),contact pressure,welding time,welding distance.

3.2.1.2 Effect ofpigments

The effect of different pigments was studied with Hostaform C 9021. From fig. 9 it can be seen that - given thesame welding conditions - all the pigmented formulationstested may be expected to provide approximately thesame level of joint strength.

Fig. 9: Effect of different pigments in HostaformC 9021 on the strength of welded joints

Fig. 10: Strength of welded joints in modifiedHostaform grades

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d Hostaform C 9021 GV 1/30e Hostaform C 9021 M

I = range of scatter

U = range of scatter

The large range of scatter observed with grey 39 and the

dark shades blue and black can be reduced by adjustingamplitude, for example. In especially critical cases, the

strength level can be raised by cutting down the pigmentcontent. This can be achieved by adding natural granules.The effect of special shades should be checked in pre

liminary trials.

3.2.1.3 Effect of reinforcing materials and elastomeradditions

Modification of Hoechst engineering plastics leads to

differences in the strength properties of ultrasonic welds,depending on the type of additive and/or reinforcingmaterial used. Fig. 10 shows this using the example of

modified Hostaform grades as compared with the basic

grade C 9021; fig. 11 shows it with Hostacom andHostalen PP.

The glass fibres in Hostaform C 9021 GV 1/30 and theHostaflon (PTFE) content in Hostaform C 9021 TF

reduce the strength of welded joints under comparableconditions. This loss in strength may be countered byincreasing the area of the joint surfaces.

Experience has shown that reinforced products requiredifferent welding conditions from those used for the basic

material, i. e. longer welding times and in some cases

smaller amplitudes and accordingly slightly highercontact pressures.

Fig. 11: Strength of welded joints in Hostacom andHostalen PP grades

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Thermoplastics impact-modified with elastomer additives

are more difficult to weld than the unmodified basic

grades. Suitability for welding depends on the elastomer

content. In any case, other welding methods such as hot

plate welding and vibration welding should be considered.

The joint strength of impact modified grades is slightlylower. This reduction may be countered by increasingthe area of the joint and/or by higher energy input (longer welding time).

As far as weld geometry is concerned, the same pointsapply as for the non-reinforced material.

3.2.2 Effect ofmouldedpart design 3.2.3.1 Requirements for the welding equipment

The parts to be welded must be dimensionally accurate

and as far as possible free from internal stresses.

To achieve this, the rules of precision injection mouldingshould be observed. Recommended processing conditions are given in the relevant Hoechst product brochures(see 10. Literature).

To ensure high quality mouldings, the following pointsare important:

correct location and cross-section of the gate for the

particular material and moulding,optimum processing conditions, in particular the rightmelt and mould temperatures,optimum mould temperature control,avoid multi-cavity production of identical articles,take into account post-shrinkage to ensure dimen

sionally accurate mouldings,do not weld parts immediately after injection moulding; a delay of at least 24 hours is recommended.

3.2.3 Welding equipment and welding conditions

Correct selection of welding conditions is of great importance for weld quality. It is vital for the welding equipment to operate reliably and for welding parameters to

be consistent with the jointing task. The quality of the

welding tool and jig is equally important.

The welding equipment has to meet a number of requirements:

high repeatability of results,sensitive control,sufficiently high output reserve,

contact pressure, welding time and hold time must

be infinitely variable,time- and stroke-dependent control should be

possible,the possibility of choosing between time-, stroke- and

energy-control operating modes extends the area of

application.

3.2.3.2 Effect ofwelding conditions

Optimum welding results can only be obtained if the

welding parameters amplitude, contact pressure, weldingtime and hold time are suitable for the material and joint.In this context it should be noted that:

The ultrasonic energy introduced (welding heat) andthe contact pressure should be carefully balanced to

ensure that there is sufficient melt flow in the weldingzone for welding but to avoid squeezing more meltthan necessary out of the welding zone.

The risk of thermal degradation of the mouldingmust be absolutely avoided, if necessary by reducingwelding time.

Prolonged welding times, excessive contact pressureor unfavourable positioning of the joint can lead to

damaged mouldings. This may not be apparent imme

diately after welding but can cause failure at a later

stage during service (creep effect).

4. Procedure for optimizingwelding conditions

Selection of welding conditions is governed by the typeof plastic, the geometry of the component, the positionand design of the joint and not least by the equipmentavailable. As a rule, welding conditions must be optimized in preliminary trials. Optimization often has to

be carried out in several stages. Corrections to the mould

ing or joint surfaces are costly and time-consuming. It

is therefore advisable not to harden the injection mouldsat this stage to make it easier to effect any corrections.

Adjustment of welding equipment parameters, on theother hand, causes fewer problems.

Stages in the optimization of welding conditions:

Stage 1: Selecting the amplitude

The vibration amplitude has to be matched to the particular material and welding problem. This is most easilyachieved by carrying out preliminary trials with different

amplitude transformers (see. fig. 1). For welding Hoechst

engineering plastics, amplitudes of 10 to 30 //m are nor

mally used.

Stage 2: Selecting the contact pressure

The contact pressure has to be matched to the amplitude.It should be such that energy transmission is not impeded.

General rule:

High amplitude - low contact pressurelow amplitude - high contact pressure.

Stage 3 : Welding time (ultrasonic exposure time)

Only a few preliminary trials are required to determine

welding time. The criterion is the time taken by the top

part to penetrate the required depth into the bottom part.Generally speaking, the welding time is less than 1

second. In practice, welding time is increasingly beingstroke-controlled to improve reliability.

Note: Prolonged welding times - which may result in

damage to the component - are often necessary if the

generator output is not sufficient and/or the bottom partvibrates in sympathy. In many cases, this problem can beremedied by supporting the bottom part if possible rightup to joint height (using a jig to hold the bottom part, see

fig. 12). Split jigs are often used for this purpose.

Fig. 12: Correct design of jig to hold the bottom part(principle)

1 horn2 top part3 bottom part4 jig

'///////////À////////////

Stage 4: Hold time

The hold time (cooling time) is normally between 0.5

and 2 s. It should be established in preliminary trials. In

critical applications, the following additional measures

are worth considering:

start the horn vibrating before it is applied to the

top part,apply slight pressure as the horn starts to vibrate,elastic jig mounts,use clamps and damping devices with thin-walled

components (to reduce diaphragm effect, see also

fig. 4).

The sum of the welding time and hold times gives the

welding cycle time (see also section 9.6). This is normally1 to 3 s. To this must be added the time for placing and

removing the joint parts. If these operations are carried

out manually, experience has shown that the total cycletime is increased by about 5 to 10 seconds. The high cost

effectiveness of ultrasonic welding is therefore fully realized

on automatic machines where cycle times of 5 seconds are

rarely exceeded. The choice of the most suitable machine

is a matter for discussion with the machinery manufac

turer. Welding machines with adequate output reserve

and welding data control are an advantage. They make

production more reliable.

10

5. Designing the joint

In ultrasonic welding, the joints may have various designsdepending on the function of the weld. The surfaces mustbe provided with energy directors. The shape and size ofthe energy directors may be freely selected within certain

limits, i. e. several alternative designs of joint are often

possible in the same situation.

The following basic designs are possible:

joints with conical and knob-shaped energy directors,joints with roof-shaped energy directors,pinch welds (edge contact).

Figs. 15 to 19 show some successful joint designs with roof-

shaped energy directors. Their dimensions may be alteredwithin certain limits. Special shapes are also possible.

Fig. 14: Roof-shaped energy director

5.1 Differentjoint designs

5.1.1 Joints with conical and knob-shapedenergy directors

Energy directors of this type (fig. 13) are used for joiningcomponents with relatively flat joint surfaces. They are

not suitable for sealing welds.

Fig. 13: Conical energy directors

=60 to 90 h = 0.5 to 1.0 mm

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5.1.2 Joints with roof-shaped energy directors

Joints with roof-shaped energy directors (fig. 14) can beused for nearly all component dimensions. The energydirector has an angle a of 60 to 90; the height h can

be varied between 0.3 and 1 mm (in special cases up to

2 mm) according to requirements.

A symmetrically positioned energy director is preferableto an asymmetrically positioned director. It should contact

the opposing joint surface as near as possible to the centre.

In special cases, several small energy directors may beused instead of one large director. They may be offsetand of different heights.

Fig. 15: Top part with inside alignment piece. Theweld is concealed on the inside but melt can escapetowards the outside

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0.05 to 0.1

Fig. 16: Top part with outside alignment piece. Theweld is concealed on the outside but melt can escapetowards the inside

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Fig. 17: Top part with alignment pieces on both sides.Because of the high dimensional accuracy required,should preferably only be used for relatively small

parts.

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0.05 to 0.1

5.1.2.1 Weld design for larger components

Fig. 18: With this joint design relatively large components can be welded. The horn is placed on the edgeof the top part. The edge of the bottom part is supported by the jig. An alignment piece on the top part or

bottom part can conceal the weld on either the insideor the outside. This weld design is very suitable forHostacom (reinforced PP).

Fig. 19: Top part with inside alignment piece and asymmetrical energy director. This design is particularlysuitable for welding hard, amorphous and partiallycrystalline plastics.

5.1.3 Joint designs for pinch welds

Pinch welds are preferred for seal welding hard, partiallycrystalline plastics. The parts must be made to close tolerances and fit together with very little clearance. The sidewalls of the bottom part should be supported up to weld

height (figs. 20 to 23).

Some successful joint designs for pinch welds are shownin figs. 21 to 23.

Fig. 20: Principle of joint design for pinch welds

0.05 to 0.1

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Fig. 21: Joint designs for single pinch welds

12

5.1.3.1 Double pinch weld with symmetricaljoint surfaces

Fig. 22: Joint designs for double pinch welds (a) with and (b) without an energy director on the bottom part.Because of the high dimensional accuracy required, should preferably be used only for parts made to close dimen

sional tolerances.

0.3 to 0.4

5.1.3.2 Double pinch weld with asymmetricaljointsurfaces

Fig. 23 : Joint designs for double pinch welds (a) withand (b) without an energy director on the bottom part.The second pinch weld is only formed after the top

part has slightly settled down on the bottom part.Because of the high dimensional accuracy required,should be used only for relatively small parts.

The "mortise and tenon" weld (fig. 24) is used for jointswhich have to be strong but need not be sealed. Much

the same criteria apply in designing this weld as with the

other types of weld discussed. In special cases sealingwelds can be obtained by incorporating elastic sealingelements.

Fig. 24: Joint designs for mortise and tenon weld

preferredweld form

13

6. Notes on ultrasonic weldingof mouldedparts made fromHoechst engineering plastics

6.1 Hostaform (POM)

Hostaform mouldings can be welded at close range and- provided suitable geometric requirements are met, i. e.low loss energy transfer to the joint surface - at longrange too. The attainable joint strength satisfies mostpractical requirements. Good welding results are obtainedwhen the joint parts are rigidly designed and the horn is

applied perpendicularly above the joint surface. A pointto watch is the rapid plasticization (transition from solidto melt) of the joint zone when the ultrasonic horn is

applied. The risk of melt beeing squeezed out of the jointcan be countered by low contact pressure. Hostaformcan be successfully welded at amplitudes between 20 and

40,Mm.

For sealing welds, single and double pinch welds accordingto figs. 20 to 23 can be selected. When welding pans with

larger dimensions (from about 60 mm diameter upwards),joint surfaces with roof-shaped energy directors or jointdesigns in accordance with fig. 18 are preferred.

The minimum height of the energy director should be0.3 mm. As a rule, the height of the energy directorshould be 1/5 to 1/10 of the base wall thickness.

The alternating strains introduced into the moulding bythe horn can in unfavourable circumstances lead to themelt separating from the solid. Even if this occurs veryrarely and usually only at isolated points it neverthelessreduces joint strength and impairs sealing welds. Melt

separation such as this tends to occur where free sinkingof one part into the other is restricted at some point. Itis therefore important at the planning stage to preventthese problems through suitable design of the joint contours. At the same time, the sink-in depth should be suit

ably limited through the provision of horn travel control.

Figs. 25 and 26 show two examples of how the risk ofmelt separation can be countered by suitable design ofthe joint contours, i. e. free sinking-in must be ensured.

Fig. 25: Minimum gap after welding in a pinch weld

minimum gapafter welding0.1 mm i

Fig. 26: Minimum gap after welding in a butt weld

minimum gapafter welding0.1 mm

The Hostaform grades differ in molecular weight andflow behaviour. The effect of these properties on weldingbehaviour was tested. The test specimens used were can-

shaped with an outside diameter of 30 mm and a wallthickness of 3 mm. A lid was welded onto the can withthe joint designed as a double pinch weld (the can and lidwere made from the same material).

Figs. 27 shows breaking loads determined on specimensproduced from the Hostaform basic grades (melt index

range studied MFR 190/2.16 : 2.5 to 48 g/10 min). Onlycans and lids made from the same Hostaform grade were

welded together. When welding moulded parts made fromdifferent Hostaform grades, lower weld quality can be

expected. The suitability of such welds for the applicationshould be tested in each particular case.

14

Fig. 27 shows that the strength of welded joints dependssignificantly on welding time. The higher values (right-hand bar) were obtained with the longer welding time

(increase from 0.6 to 1.0 s).

Fig. 27: Effect of the melt viscosity of Hostaform basic

grades on the strength of welded joints

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C 52021

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C 13021

(13)

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C9021

(9.5)C2521

(2.5)Basic grades

(The figures in brackets are the melt index valuesMFR/190/2.16 in g/10 min)Frequency 20 kHzAmplitude 30 1* mWelding pressure 1.8 barWelding time 0.6 sec (left bar)

1.0 sec (right bar)Weld design double pinch weldGenerator output 700 W

Fig. 28: Effect of additives in modified Hostaformgrades on welded joint strength

"iJÜÜ&cC

'Si

ECQ

8000

N

6000

4000

2000

0

1

IE

-

C9021GV 1/30

(4.5)

pC9021GV 3/30

(9)Reinforced grades

1

:

S 27073

(22)

If]S 27076

(17)

C

F1 -

S 9063

(9)

S 9064

(8)Increased impact grades

Studies of test specimens made from reinforced and

impact modified Hostaform grades show generally satis

factory welding behaviour except for Hostaform S 27076.The breaking load values attained with 1 sec. weldingtimes roughly correspond to those for the basic grades,fig. 28. Prolongation of welding time leads to a considerable increase in breaking load. The strength loss in thecase of Hostaform S 27076 is due to the higher elastomercontent.

6.2 Hostacom (reinforced PP)

Hostacom and Hostalen PP grades can only be welded at

close range because of their high damping capacity.Studies showed that with the materials indicated in fig.29 homogeneous welds can be obtained. Joint strength as

compared with the parent material depends on the typeand amount of reinforcing material used. Fig. 29 showshow these influences affect joint strength.^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^m

Fig. 29: Joint strength of ultrasonically welded test

specimens made from Hostalen PPN 1060 andHostacom grades

4000

N

^3000

cs

_ouc.5 2000rtOJ

<a1000

0PPN 1060

non-reinf.

G2N01

,

G3N01

E

,

M2N01 M4N01

reinforced

FrequencyAmplitudeWelding pressureWelding timeWeld designGenerator output

20 kHz30, m1.8 bar1.0 sec

double pinch weld700 W

(The figures in brackets are the melt index valuesMFR/190/2.16 in g/10 min)Frequency 20 kHzAmplitude 30, mWelding pressure 1.8 barWelding time 0.6 sec (left bar)

1 .0 sec (right bar)Weld design double pinch weldGenerator output 700 W

15

6.3 Celanex (PB T)

The breaking load values attainable with specimens madefrom Celanex are shown in fig. 30. Even long-rangewelds (up to 25 mm distance between horn and joint sur

faces) give serviceable results.

Fig. 30: Joint strength of ultrasonically welded test

specimens made from various Celanex grades

8000

N

6000

1g" 4000

1so 2000

02500

non-reinf.

~

2300GV 1/30

m

2360GV 1/30 H.

reinforced

FrequencyAmplitudeWelding pressureWelding time

Weld designGenerator output

20kHz30 fim1.8 bar0.6 sec (left bar)1 .0 sec (right bar}double pinch weld700 W

Celanex, like Hostaform, plasticizes (changes from solid

to melt) rapidly when the ultrasonic horn is applied.Here again there is a risk of melt being squeezed from

the joint at excessive contact pressures.

7. Ultrasonic assembly ofperformance polymers

The Hoechst performance polymers Fortran (PPS) andVectra (LCP) can generally be joined by ultrasonic

assembly methods such as welding, riveting, flanging and

staking. Metal inserts can be ultrasonically embedded.In most cases, the guidelines and notes relating to ultrasonic welding of the engineering plastics described are

also applicable to the performance polymers. It should beremembered however that high filler contents can cause

damage to moldings during transmission of ultrasonic

energy. In such cases, it is advisable to check whether the

problem can be effectively remedied by higher frequenciesor smaller amplitudes.

In critical cases, close cooperation between the user, equipment manufacturer and material producer is essential.

7.1 Fortron (PPS)

Fortran is suitable for both near- and far-field ultrasonic

welding. However, because of the relatively brittle-hardbehaviour of the material, it should be borne in mind that

the alternating strains which have to be absorbed by the

joint parts can lead to localized damage. To avoid this,special precautions need to be taken in terms of correct

component design for the material and weld and corre

spondingly optimized equipment settings. Since these

measures have to be specially adapted to the component,we recommend early contact with the equipment manufacturer and material supplier.

Additions of reinforcing material up to 40% still permitgood welding results. Under mechanical load, fracture

usually occurs outside the weld. With higher proportionsof reinforcing material, however, weldability deteriorates.

Tapered pinch welds with a welding distance of over

1 mm can if necessary be made gas-tight.

16

7.2 Vectra (LCP)

The welding behaviour of Vectra is uniquely influenced

by its characteristic material properties and molecularorientation in the joint parts. Particularly good results are

obtained if the weld runs in the direction of orientation.

As trials on models have shown, these requirements can

best be met by pinch welds with slightly tapered jointsurfaces (angle of inclination 10 to 15).

Ultrasonically welded Vectra moldings are gas-tight.

Good energy transmission is obtained in near-field weld

ing. With far-field welding, thicker walls are generallyrecommended for energy transmission.

8. Other ultrasonic assemblymethods

Ultrasonics can be used to plasticize and re-form mould

ings. This possibility is used in riveting, flanging and

staking. The advantage of ultrasonic methods as comparedwith re-forming with a hot die is that the ultrasonic horn

remains cold and so can also assume the function of the

cooling die.

8.1 Riveting

In riveting, the vibration energy at the rivet shaft endis converted into heat. The plasticization initiated in this

way is allowed to continue until the rivet head is formed.The ultrasonic horn assumes the function of the rivetingdie and is produced in the desired shape of the rivet head.

Single and multiple riveting can be carried out in one

operation.

The riveting time (welding time) depends on the material

and the rivet shaft diameter. It ranges between 0.5 and2 sec. In many cases, it is advisable to work with clamps.The following points should be borne in mind when rivet

ing:

the projecting end of the rivet shaft should be ofsufficient volume for the proposed rivet head,the ultrasonic horn should be lowered slowly,contact pressure should be lower and amplitudegenerally higher than in ultrasonic welding,the horn should be held in position until the rivet

head freezes,the end of the horn may be subject to wear (especiallyin the case of glass fibre reinforced plastics).

The rivet pin is in most cases an integral part of the

moulding. The point where it joints the main body of the

moulding should be radiused as generously as possible to

prevent plasticization or breakage. Shaft design accordingto fig. 31 H have proved successful. The part to be rive

ted to the plastic is provided with a slightly oversized

receiving hole for the rivet shaft (clearance fit). The rivet

pin projection length and rivet head design depend on

the material being riveted,the required strength,the rivet shaft dimension,the dimensional tolerance (in multiple riveting).

17

Fig. 3 1 : Recommended rivet pin diameters and rivet head designs

Diagram showinghorn design, workpieceand rivet head

L^,"~"f2Zï^ë^

rL-fc-^> \

XXXX./.^. XXXN

/////X////À -1

^k050 I

4

\XX XXN' Xkx N. X \ ^|'//////////A -i\

si r

FK| j

_4L5diL^*J

IXXXXXXT XIX

V/////Y/\

\'Y<k/

m

ö

^75 d

XR -^i*-/ ^>B3 !

*\\N-Y -ni//X/ .of

3'

r-^-T-x-^l 1

/R ^/ ?

m

t^>^w>^_a

/vî4?^.tx \\\ ^^/ti..^

<^l 1

\x\^Y/////À/////

\

R\lK l

\\V - ;fy

a

/A\\\

/////%////,

, i .<T<A ' C^

^

Head

design

A

C

E

G

Diagram showinghorn design, workpieceand rivet head

J s^k*-/y y/ f

'////Y////'""i Yr~~\gmY//////////,

\

^i /

^~%~-/i/'////</////,

-*H 2dJ-,-*v xxxxrxixxxxx'//////////A

\

$R

"*ttfe^r>xXkg

V////*/////.^->-

IvXXXXY ^>^x> XN

V/;/7/\/////s\

?\ovO

CN

ttT3

1

iTJ\o

t

3

1ü

1

_Jl/RsssEfes///7)Cr///.

fa /Rx^^i^Y///////,

1

Head

design

B

D

F

H

Rivet pindiameter

ri "> 1 Ç

d>2

d>0.5

18

Fig. 31 shows some frequently used rivet head designs.Rivet head designs A and B are preferably employed for

thin rivet pins up to about 3 mm diameter. Head designsC and D have proved particularly successful. In these

designs, the contact surface between the horn and rivet

pin is through the central tip which must be applied cen

trally and initially represents a very small area. The ultra

sonic energy is introduced through this area. Head designD is preferred because of the good strength values it gives.In design E, the horn face is knurled. This design has

proved successful for single, and particularly, for multipleriveting. It enables positional inaccuracies between the

horn and rivet pin and dimensional tolerances in the

spacing between a number of rivets to be accommodated.If large rivet pin diameters are required, it is advisable

to use hollow pins, fig. 31 design G or several thin pinsto avoid sink marks when injection moulding the parts.

In riveting glass fibre reinforced thermoplastics, a higherultrasonic output is required than for the non-reinforcedmaterial.

Since the rivet horns are subject to relatively severe wear

with glass reinforced plastics, the horn surface must beof wear resistant design (e.g. carbide tipped).

In special cases, it might be advisable to check whetherhot riveting would give better results.

In riveting mouldings made from Hostaform and

Celanex, it is important not only to optimize rivet head

design but to select riveting conditions very carefully.Designs C, D and E, fig. 31, should preferably be used.

Good results are also obtained with head designs C and

E (fig. 31) when riveting the ultrahigh molecular weightmaterial Hostalen GUR. The following conditions are

recommended:

high generator output,high amplitude,contact pressure commensurate with amplitude,low horn descent speed,welding time commensurate with the volume of

material to be plasticized (time required to convert

the projecting rivet pin to a rivet head),long hold time (=2 s).

8.2 Flanging

As in metal processing, mouldings made from engineeringplastics can be flanged. In this way, plastic componentscan be joined to each other and to components made from

other materials. The horn must be appropriately profiledfor the task in hand to plasticize and re-form edges, pinsprojections or other fixing aids.

Ultrasonic flanging is very economic. Processing times

are comparable with the normal cycles for ultrasonic

welding of mouldings. When flanging over glass components, the horn should not touch the glass part.

Figs. 32 and 33 show examples of inside and outside

flanging.

Fig. 32: Inside flanging, fixing a metal plate in a plastichousing

Before flanging After flanging

1 Plastic housing2 Ultrasonic horn3 Metal plate to be fixed

Fig. 33: Outside flanging, fixing a plastic pipe stub into

a container base

Before flanging After flanging

1 Metal base2 Ultrasonic horn3 Pipe stub to be attached

19

83 Staking

Staking can be carried out relatively easily by the ultrasonic technique. Staking is a jointing method similar to

flanging or riveting in which the plasticized material isforced into recesses, undercuts or holes so creating a

non-detachable joint, fig. 34.

Fig. 34: Securing parts together by staking

re-forming recessing

metal part

plastic part

8.4 Insertion of metal parts

Threaded inserts, set screws or other metal parts can beembedded in specially provided holes or recesses with theaid of ultrasonics. Depending on the design of the metal

parts, high anti-rotation and pull-out resistance can beachieved.

Fig. 35 shows some examples.

With this jointing technique, the following points shouldbe observed.

Straight insertion of the metal part can be ensured by providing a guide hole which is about 0.1 to 0.2 mm largerin diameter than the metal part. The metal inserts mustbe guided. The boss should have a radius of R > 0.2 mm

at the junction with the main body of the plastic part,fig. 35.

The receiving hole must be slightly smaller than themetal inserts, table 1.

When tapered metal parts are to be embedded in cylindrical receiving holes, the metal part should be sunk about

halfway into the receiving hole. The undersizing of the

receiving hole should be sufficient to provide a volumeof plasticized material at least equivalent to the volumeof the undercuts or knurling in the metal part.

In the case of blind holes, the receiving hole must be at

least 2 to 3 mm deeper than the insertion depth of thematerial part in order to accommodate the displaced molten plastic.

The wall thickness of the boss should be at least 2 mm.

During insertion, the amplitude should be as low as possible to avoid damaging either the metal insert or the

plastic wall.

It is an advantage to start the horn vibrating before ap

plying it to the part or to introduce the ultrasonic energyimmediately after applying very slight contact pressure.The horn descent rate should be slow. Ultrasonic application should only be continued until the metal part is fullyinserted. During insertion, metal abrasion can be expected.

Fig. 35: Plastic parts with integrally moulded boss to

receive metal parts

R>0.2

20

Table 1: Recommended receiving hole diameters for threaded inserts 1 and 2 (dimensions in mm)

Metricthread

M3

M4

M5

M6

M8

Metricthread

M3

M4

M5

M6

M8

Length of

bushing1

5.5

7.5

9.0

10.0

12.0

Length of

bushing1

5.8

8.2

9.5

12.7

12.7

Dian

Dl

4.0

5.2

6.4

7.7

9.7

Diari

Dl

3.9

5.5

6.3

7.9

9.5

icter

D2

4.7

6.15

7.35

8.75

11.3

icter

D2

4.7

6.3

7.1

8.7

10.2

Receivinghole diameter

(guide values)

4.3

5.65

6.85

8.25

10.8

Receivinghole diameter

(guide values)

4.0

5.6

6.4

8.0

9.6

Threaded insert 1

D2

1 1 II

1 1Dl-l

Threaded insert 2

l

\

\\.

-D2

1

11Ëi

-Dl-

T

21

9. Examples ofapplications9.1 Sewing machine control part

sliding cam top part

; bottom part

This part made of Hostaform C 13021 is difficult to

weld. Correct horn/part contact was obtained witha suitably contoured horn.

9.2 Time control mechanism for a toaster

housi

a<:

- -H*,-^s

0.05

\

\*

)0\\

This time control mechanism enables toasting time to

be set exactly every time to suit individual taste. The

housing and top are injection moulded from Hostaform C 13021. The top is welded to the housing to

form an air-tight seal.

9.3 Disposable cigarette lighter

top-tf 0.05 to 0.1

45tank

This lighter comprises a tank with welded-on top. The

components are under internal pressure stress. Theyare made from Hostaform C 27021.

22

9.4 Pneumatic control element

0.05 to 0.1

These pneumatic control elements made from Hosta-form C 9021 are used to control pressure, quantityand direction. In each valve body there are severalvalve pistons which move in a cylindrical bore. After

assembly, the bores are sealed with disc-like caps byultrasonic welding.

9.5 Mixer tap regulator

housing4- 0.05 to 0.1

0.4

These injection moulded Hostaform C 13021 regulators are used in single-lever-operated mixer taps. Afterinsertion of ceramic sealing washers, the top and hous

ing are welded together to form a liquid-tight seal.

23

9.6 Example ofwelding cycle time calculation -ir\ J îfpYsltlJYP

A gas cigarette lighter tank and top are to be ultrasonicallywelded. A rotary table machine with standard welding G. Menges, H. Potente: Schallfelder und Energieum-equipment is available. The jig is the split type and is Setzung beim Ultraschallschweißen von Kunststoffen.closed pneumatically. The whole process, including place- Kunststoffe, vol. 59, 1969, no. 6.

mem of the parts to be welded, is automated.

H. Potente: Thesis, TH Aachen.Determination of cycle time: [s]O placement of the tank in the jig, including G. Menges, H. Potente, D. Pieschel: Vorhersage der

pneumatic jig closure 1.5 Schweißbarkeit von Kunststoffen aus bekannten Werk-O transport of the top 1.0 Stoffkennwerten. Kautschuk und Gummi, Kunststoffe,O positioning of the top 0.5 vol. 25. no. 6/1972.

advance of rotary table machine 0.5 R. Martin: Gasfeuerzeugtanks aus Hostaform,application of horn 0.5 Plastverarbeiter 1978, no. 8, pp. 419 - 424.

welding time 0.5

hold time 1.0 H. Vowinkel: Ultraschallschweißen von Formteilen aus

removal of horn 0.5 Acetalcopolymerisat, Industrie-Anzeiger 93/1980.O ejection of welded part < 0.5

N. El Barbari: Thesis, TH Aachen: UltraschallschweißenThe total time for the operations marked with () = von Thermoplasten, Möglichkeiten der Einsatzoptimie-3.0 s = cycle time, i.e. in an eight-hour day, output is rung.9600.

Product brochure "Hoechst Plastics, Hostaform" B 244.The operations marked with (O) run parallel to the weld

ing operation and thus have no effect on cycle time. Product brochure "Hoechst Plastics, Hostacom (reinforced PP)", H 703.

Product brochure "Hoechst Plastics, Celanex, Vandar,Impet", B 243.

Product brochure "Fortron (PPS)", B 240.

Product brochure "Vectra (LCP)", B 241.

ZVEI brochure: "Ultrasonic assembly of thermoplasticmouldings and semi-finished products",ZVEI, Stresemannallee 19

D-60596 Frankfurt a. M.

DVS Data Sheets: 2216 part 1 - 5

24

Useful addresses:

Branson, Ultraschall GmbH,Waldstraße 53 - 55, D-63128 Dietzenbach

Herrmann Ultraschalltechnik,Descostraße, D-76307 Karlsbad-Ittersbach

KLN - Ultraschall - GmbH,Siegfriedstraße 124, D-64646 Heppenheim

KVT Bielefeld, Gesellschaft fürKunststoff-Verbindungstechnik mbH,Werkering 6, D-33609 Bielefeld

Rinco Ultrasonics,CH-8590 Romanshorn/Schweiz

Telsonic Ultraschallgeräte GmbH,Gartenstraße 17, D-88212 Ravensburg

Telsonic AG,Industriestraße, CH-9552 Bronschhofen/Schweiz

Engineering plasticsDesign Calculations Applications

Publications so far in this series:

A. Engineering plasticsA. 1.1 Grades and properties - HostaformA. 1.2 Grades and properties - HostacomA. 1.4 Grades and properties - Hostalen GUR

A. 1.5 Grades and properties - Celanex,Vandar, Impet

A.2.1 Calculation principlesA.2.2 Hostaform - Characteristic values and

calculation examplesA.2.3 Hostacom - Characteristic values and

calculation examples

B. Design of technical mouldingsB.I.I Spur gears with gearwheels made from

Hostaform, Celanex and Hostalen GUR

B.2.2 Worm gears with worm wheels made fromHostaform

B.3.1 Design calculations for snap-fit joints in

plastic partsB.3.2 Fastening with metal screws

B.3.3 Plastic parts with integrally moulded threadsB.3.4 Design calculations for press-fit jointsB.3.5 Integral hinges in engineering plasticsB.3.7 Ultrasonic welding and assembly of

engineering plastics

C. Production of technical mouldingsC.2.1 Hot runner system - Indirectly heated,

thermally conductive torpedoC.2.2 Hot runner system - Indirectly heated,

thermally conductive torpedoDesign principles and examples of mouldsfor processing Hostaform

C.3.1 Machining HostaformC.3.3 Design of mouldings made from

engineering plasticsC.3.4 Guidelines for the design of mouldings

in engineering plasticsC.3.5 Outsert moulding with Hostaform

25

In this technical information brochure, Hoechst aims to

provide useful information for designers who want to

exploit the properties of engineering polymers such as

Hostaform. In addition, our staff will be glad to advise

you on materials, design and processing.

This information is based on our present state of knowl

edge and is intended to provide general notes on our

products and their uses. It should not therefore be con

strued as guaranteeing specific properties of the productsdescribed or their suitability for a particular application.Any existing industrial property rights must be observed.The quality of our products is guaranteed under our

General Conditions of Sale.

Applications involving the use of the Hoechst materialsHostaform, Celanex, Hostalen GUR, Fortron andVectra are developments or products of the plasticsprocessing industry. Hoechst as supplier of the startingmaterial will be pleased to give the names of processorsof plastics for technical applications.

© Copyright by Hoechst Aktiengesellschaft

Issued in August 199677th edition

26

Hostaform®, Celcon®

polyoxymethylene copolymer (POM)

Celanex®

thermoplastic polyester (PBT)

Impet®

thermoplastic polyester (PET)

Vandar® thermoplastic polyester alloys

Riteflex®

thermoplastic polyester elastomer (TPE-E)

Vectra®

liquid crystal polymer (LCP)

Fortron®

polyphenylene sulfide (PPS)

Celstran®, Compel® long fiber reinforced thermoplastics (LFRT)

GUR®

ultra-high molecular weight polyethylene (PE-UHMW)

EuropeTicona GmbHInformation ServiceTel.: +49 (0) 180-5 84 26 62 (Germany) +49 (0) 69-30 51 62 99 (Europe)Fax: +49 (0) 180-2 02 12 02eMail: infoservice@ticona.deInternet: www.ticona.com

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